Light-emitting element having nitride semiconductor multiquantum barrier, and process for production thereof

Abstract

An Al 0.95 Ga 0.05 N:Mg (25 nm) single electron barrier can stop electrons having energy levels lower than the barrier height. Meanwhile, a 5-layer Al 0.95 Ga 0.05 N (4 nm)/Al 0.77 Ga 0.23 N (2 nm) MQB has quantum-mechanical effects so as to stop electrons having energy levels higher than the barrier height. Thus, electrons having energy levels higher than the barrier height can be blocked by making use of multiquantum MQB effects upon electrons. The present inventors found that the use of an MQB allows blocking of electrons having higher energy levels than those blocked using an SQB. In particular, for InAlGaN-based ultraviolet elements, AlGaN having the composition similar to that of AlN is used; however, it is difficult to realize a barrier having the barrier height exceeding that of AlN. Therefore, MQB effects are very important. Accordingly, it becomes possible to provide element technology for further improving deep UV light emission intensity using, as a light-emitting layer material, an AlGaInN-based material and, in particular, an AlGaN-based material.

The invention claimed is: 
     
       1. A nitride semiconductor light-emitting element that emits light at a wavelength of 220 to 390 nm, comprising:
 an Al x Ga 1-x N (0<x<1) buffer layer formed on a substrate; 
 an n-type In x Al y Ga 1-x-y N (0<x<0.1, 0<y<1) layer formed on the Al x Ga 1-x N buffer layer; 
 a quantum-well light-emitting layer comprising an In x1 Al y1 Ga 1-x1-y1 N (0<x1<0.5, 0<y1<1) quantum well layer and an In x2 Al y2 Ga 1-x2-y2 N (0<x2<0.3, 0<y2<1, x1>x2, y1<y2) barrier layer formed on the n-type InAlGaN layer; 
 a p-type In x Al y Ga 1-x-y N (0<x<0.1, 0<y<1) layer formed on the InAlGaN quantum-well light-emitting layer; and 
 a multiquantum-barrier electron-blocking layer formed on the p-type InAlGaN layer, 
 wherein the multiquantum-barrier electron-blocking layer is formed by alternately layering In x1 Al y1 Ga 1-x1-y1 N (0<x1<0.1, 0<y1<1) barrier layers and In x2 Al y2 Ga 1-x2-y2 N (0<x2<0.3, 0<y2<1, x1<x2, y1>y2) valley layers for the same number of periods or a 1st number of periods and a 2nd number of periods that differs from the 1st number of periods; and 
 wherein the number of periods increases or decreases in a stepwise manner from the quantum-well light-emitting layer side to the multiquantum-barrier electron-blocking layer side. 
 
     
     
       2. A near-ultraviolet, purple, blue, or green nitride semiconductor light-emitting element that emits light at a wavelength of 390 to 550 nm, comprising:
 an Al x Ga 1-x N (0<x<1) buffer layer formed on a substrate; 
 an n-type In x Al y Ga 1-x-y N (0<x<0.1, 0<y<1) layer formed on the Al x Ga 1-x N buffer layer; 
 a quantum-well light-emitting layer comprising an In x1 Al y1 Ga 1-x1-y1 N (0<x1<0.5, 0<y1<1) quantum well layer and an In x2 Al y2 Ga 1-x2-y2 N (0<x2<0.3, 0<y2<1, x1>x2, y1<y2) barrier layer formed on the n-type InAlGaN layer; 
 a p-type In x Al y Ga 1-x-y N (0<x<0.1, 0<y<1) layer formed on the InAlGaN quantum-well light-emitting layer; and 
 a multiquantum-barrier electron-blocking layer formed on the p-type InAlGaN layer, 
 wherein 
 the multiquantum-barrier electron-blocking layer is formed by alternately layering In x1 Al y1 Ga 1-x1-y1 N (0<x1<0.1, 0<y1<1) barrier layers and In x2 Al y2 Ga 1-x2-y2 N (0<x2<0.3, 0<y2<1, x1<x2, y1>y2) valley layers for a given number of periods or a 1st number of periods and a 2nd number of periods that differs from the 1st number of periods; 
 wherein the number of periods increases or decreases in a stepwise manner from the quantum-well light-emitting layer side to the multiquantum-barrier electron-blocking layer side. 
 
     
     
       3. A nitride semiconductor light-emitting element that emits light at a wavelength of 220 to 390 nm, comprising:
 an Al x Ga 1-x N (0<x<1) buffer layer formed on a substrate; 
 an n-type InxAl y Ga 1-x-y N (0<x<0.1, 0<y<1) layer formed on the AlxGa1−xN buffer layer; 
 a quantum-well light-emitting layer comprising an In x1 Al y1 Ga 1-x1-y1 N (0<x1<0.5, 0<y1<1) quantum well layer and an In x2 Al y2 Ga 1-x2-y2 N (0<x2<0.3, 0<y2<1, x1>x2, y1<y2) barrier layer formed on the n-type InAlGaN layer; 
 a p-type In x Al y Ga 1-x-y N (0<x<0.1, 0<y<1) layer formed on the InAlGaN quantum-well light-emitting layer; 
 wherein the multiquantum-barrier electron-blocking layer is a non-polar layer formed on an A-plane or M-plane or a layer formed on a semipolar plane. 
 
     
     
       4. A process for growing a light-emitting element structure on a group-III nitride single crystal, comprising the steps of:
 growing an Al x Ga 1-x N (0<x<1) buffer layer on a substrate; 
 growing an n-type In x Al y Ga 1-x-y N (0<x<0.1, 0<y<1) layer on the Al x Ga 1-x N buffer layer; 
 growing a quantum-well light-emitting layer comprising an In x1 Al y1 Ga 1-x1-y1 N (0<x1 
 <0.5, 0<y1<1) quantum well layer and an In x2 Al y2 Ga 1-x2-y2 N (0<x2<0.3, 0<y2<1, x1>x2, y1<y2) barrier layer on the n-type InAlGaN layer; 
 growing a p-type In x Al y Ga 1-x-y N (0<x<0.1, 0<y<1) layer on the quantum-well light-emitting layer; and 
 growing a multiquantum-barrier electron-blocking layer by alternately layering In x1 Al y1 Ga 1-x1-y1 N (0<x1<0.1, 0<y1<1) barrier layers and In x2 Al y2 Ga 1-x2-y2 N (0<x2<0.1, 0<y2<1, x1<x2, y1>y2) valley layers on the p-type InAlGaN layer 
 wherein the multiquantum-barrier electron-blocking layer is a non-polar layer formed on an A-plane or M-plane or a layer formed on a semipolar plane. 
 
     
     
       5. A nitride semiconductor light-emitting element that emits light at a wavelength of 220 to 390 nm, comprising:
 an Al x Ga 1-x N (0<x<1) buffer layer formed on a substrate; 
 an n-type InxAl y Ga 1-x-y N (0<x<0.1, 0<y<1) layer formed on the AlxGa1−xN buffer layer; 
 a quantum-well light-emitting layer comprising an In x1 Al y1 Ga 1-x1-y1 N (0<x1<0.5, 0<y1<1) quantum well layer and an In x2 Al y2 Ga 1-x2-y2 N (0<x2<0.3, 0<y2<1, x1>x2, y1<y2) barrier layer formed on the n-type InAlGaN layer; 
 a p-type In x Al y Ga 1-x-y N (0<x<0.1, 0<y<1) layer formed on the InAlGaN quantum-well light-emitting layer; and 
 a multiquantum-barrier electron-blocking layer formed on the p-type InAlGaN layer, wherein 
 the multiquantum-barrier electron-blocking layer formed on the p-type InAlGaN layer comprises a plurality of pairs of an In x1 Al y1 Ga 1-x1-y1 N (0<x1<0.1, 0<y1<1) barrier layer and an In x2 Al y2 Ga 1-x2-y2 N (0<x2<0.3, 0<y2<1, x1<x2, y1>y2) valley layer, wherein 
 a 1st pair of layers and the 2nd pair of layers are spaced apart, provided that the layer thickness of the 1st pair of layers is greater or less than the layer thickness of the 2nd pair of layers, and wherein 
 the 1st pair of layers and the 2nd pair of layers are arranged in that order from the quantum-well light-emitting layer side to the side opposite the substrate. 
 
     
     
       6. A nitride semiconductor light-emitting element that emits light at a wavelength of 220 to 390 nm, comprising:
 an Al x Ga 1-x N (0<x<1) buffer layer formed on a substrate; 
 an n-type In x Al y Ga 1-x-y N (0<x<0.1, 0<y<1) layer formed on the AlxGa1−xN buffer layer; 
 a quantum-well light-emitting layer comprising an In x1 Al y1 Ga 1-x1-y1 N (0<x1<0.5, 0<y1<1) quantum well layer and an In x2 Al y2 Ga 1-x2-y2 N (0<x2<0.3, 0<y2<1, x1>x2, y1<y2) barrier layer formed on the n-type InAlGaN layer; 
 a p-type In x Al y Ga 1-x-y N (0<x<0.1, 0<y<1) layer formed on the InAlGaN quantum-well light-emitting layer; and 
 a multiquantum-barrier electron-blocking layer formed on the p-type InAlGaN layer wherein 
 the multiquantum-barrier electron-blocking layer formed on the p-type InAlGaN layer comprises a plurality of pairs of an In x1 Al y1 Ga 1-x1-y1 N (0<x1<0.1, 0<y1<1) barrier layer and an In x2 Al y2 Ga 1-x2-y2 N (0<x2<0.3, 0<y2<1, x1<x2, y1>y2) valley layer, wherein 
 a 1st pair of layers, a 2nd pair of layers, and a 3rd pair of layers are spaced at intervals, provided that: 
 the layer thickness of the 1st pair of layers is greater than the layer thickness of the 2nd pair of layers and the layer thickness of the 2nd pair of layers is greater than the layer thickness of the 3rd pair of layers; or 
 the layer thickness of the 1st pair of layers is less than the layer thickness of the 2nd pair of layers and the layer thickness of the 2nd pair of layers is less than the layer thickness of the 3rd pair of layers, and wherein 
 the 1st, 2nd, and 3rd pairs of layers are provided in that order from the quantum-well light-emitting layer side to the side opposite the substrate. 
 
     
     
       7. The nitride semiconductor ultraviolet light-emitting element according to  claim 5 , wherein the multi-layer number of barrier layers and that of valley layers of the pair of layers are the same. 
     
     
       8. The nitride semiconductor ultraviolet light-emitting element according to  claim 5 , which is a light-emitting diode.